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Elements of the Heart: Collateral Circulation, Valves and Conduction System

by Richard Mitchell, MD

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    00:01 That's the arterial circulation.

    00:03 What about veins? Oh my god, there are veins in the heart.

    00:05 Yeah, there are, that's how we get blood back from the muscle of the heart back into the venous circulation.

    00:13 So how does this happen? Well, so there are variety of veins that more or less follow the arteries.

    00:19 They all collect into the great cardiac vein, which wraps around the back of the heart.

    00:23 And then that dumps all of its contents into the coronary sinus, which enters into the right atrium.

    00:32 So this is kind of shown here, in a slightly different view, you can see the blood coming from that great cardiac vein into the coronary sinus, and that's dumping into the right atrium just above the tricuspid valve.

    00:47 Okay, again, kind of talked about it, we're berating this point, because it's really important, there is a collateral circulation in the heart.

    00:54 So this is our right coronary artery, our left anterior descending artery, our left circumflex artery, and there are zones between them where there's collateralization, that allows making sure that we can get blood supply to all parts of the heart.

    01:09 We already talked about the collaterals that will happen at the apex.

    01:12 And we talked about those that would happen between the right posterior circulation and the left circumflex circulation.

    01:19 Okay, if we cut the heart in that transverse slice, this is generally how the parts of the heart are being perfused in 90% of us.

    01:28 Keep in mind this will be different if you have a left dominant circulation.

    01:32 So the anterior 2/3 of the septum in the anterior wall and beginning into the lateral wall, all of that in purple there is perfused by the left anterior descending circulation.

    01:44 On the lateral wall, indicated here in green is the left circumflex circulation, the entire right ventricle and the posterior left ventricle and posterior 1/3 of the septum is perfused in general by the right coronary circulation.

    01:58 So knowing this anatomy, you can predict which parts of the heart are going to be affected if there's blockage, major blockage in one of the vessels perfusing that area.

    02:10 On this slide, we are going to look at many of the valvular structures and their relationships one to another.

    02:19 By the time we finish with this slide, there are going to be words all over it.

    02:23 But we're going to do it step by step, so you'll be able to follow along.

    02:27 We're going to follow the way that blood flows through the heart.

    02:31 So we're going to begin in the upper left hand corner.

    02:34 That's what the tricuspid valve.

    02:38 Blood is coming from the inferior and superior vena cava, into the right atrium.

    02:44 The right atrium is then going to push the blood into the right ventricle through the tricuspid valve.

    02:52 It is a trileaflet there are three leaflets of the tricuspid valve, a posterior leaflet, a septal leaflet and an anterior leaflet.

    03:01 Okay.

    03:03 Just above that is where we're going to have the coronary sinus come in.

    03:06 Okay, so that gets you oriented to where we are in terms of the geography of the heart.

    03:11 Okay, that's going to allow blood to go from the right atrium of the right ventricle.

    03:14 From the right ventricle out to the lungs is the pulmonary valve.

    03:19 The pulmonary valve, again, remember sits at the most anterior portion of the heart.

    03:24 It has a tricuspid, three cusps valve, it's a semi lunar valve, we'll talk more about semilunar versus atrioventricular valves, that goes out to the lungs gets oxygenated all the blood comes back through from the left to the left atrium.

    03:40 And then between the left atrium left ventricle is going to be the mitral valve in the upper right hand corner.

    03:47 It's got just two leaflets.

    03:50 It's got a posterior leaflet and an anterior leaflet.

    03:54 Okay, so it has a slightly different structure than the other valves which have usually three cusps, or three leaflets.

    04:03 That's actually why the mitral valve is more prone to more diseases than any of the other valves.

    04:09 Interesting little factoid.

    04:11 Okay, so we have a posterior and anterior leaflet of the mitral valve, blood gets into the left ventricle, and then get squeezed out through the aortic valve.

    04:21 And the aortic valve again, normally is a three cusp valve, three cusps, and they have an anterior, we have a posterior non coronary cusp.

    04:35 We have an anterior coronary cusp that has the right coronary artery coming off it and the left anterior coronary cusp that has the left main coming off it.

    04:47 The sinuses.

    04:47 So the areas behind those cusps are called the sinuses of Valsalva.

    04:53 Alright, we've covered all the words on this slide.

    04:57 Let's look at these in a little bit more detail.

    05:00 Okay, the way that the valves work are a little bit different depending on whether you are a semilunar valve that is to say pulmonic or aortic valve, versus whether you are a tricuspid or a mitral valve, an atrioventricular valve.

    05:15 Okay.

    05:16 So, let's look at the tricuspid valve and everything I'm going to say about the tricuspid valve is also true about the mitral valve.

    05:23 These are the atrioventricular valves, they are the entry points from the atrium to the ventricles.

    05:31 The valves are dependent on the integrity of the annulus.

    05:35 The ring that holds the valve tissue, it's dependent on the integrity of the valve leaflets themselves.

    05:43 It's dependent on the chordae tendineae shown here, so thin, delicate, tendinous insertions that connect to the edge of the valve to the underlying papillary muscle.

    05:55 Papillary muscles contiguous with the right ventricular wall.

    05:59 All elements of the atrioventricular valves, whether your tricuspid or mitral must be intact in order for that valve to maintain competence.

    06:09 Okay.

    06:11 Mitral valve, same story.

    06:13 Chordae tendineae again, mitral valve, the integrity of the annulus is important.

    06:19 The integrity the valve material, the actual leaflets, important.

    06:23 The integrity of the chordae tendineae, important.

    06:26 The integrity of the papillary muscles, important.

    06:29 Integrity of the ventricular wall, important.

    06:32 And we will talk when we talk about valvular pathology in a subsequent talk, how the ventricular wall may dilate, may get expanded, and when it does it pulls on the papillary muscles which pull in the chordae tendineae which keep the valves from being able to close.

    06:47 So simply having a chamber that is abnormal, in terms of its dilation can lead to valvular dysfunction as well.

    06:55 Okay, those are atrioventricular valves.

    07:00 We'll talk briefly about the conduction system and we'll come back to this.

    07:03 So the heart is a beautiful structure, it's got all these various elements that you need to be aware of, because there's pathology associated with all of them.

    07:12 One of the beautiful elements of this is a self-beating, self-regulating tissue that has a certain conduction system that allows it to contract in an organized fashion to pump blood.

    07:26 The initial signal that says go or no go is at the sinoatrial node.

    07:30 And it's followed by activation signal at the atrioventricular node.

    07:35 We'll revisit this, we'll get in more detail in a moment.

    07:38 Okay.

    07:40 Let's look at all the elements of the heart in turn.

    07:42 So we're gonna have the myocardium, we're gonna have the valves, we're gonna have the coronary vasculature, we're gonna have the conduction system, and all of them have to work together for the heart to do its thing, which it's doing there very nicely on the left hand side, it's beating in an organized fashion to pump blood in an organized fashion at a particular pressure to the rest of the body.

    08:02 Okay.

    08:04 General things, so myocardium works fine here, the valves work fine, the coronary vasculature is fine, but what's wrong here is that we have an abnormal conduction system.

    08:13 And what's being shown in particular is atrial fibrillation.

    08:16 See that right atrium, left atrium, it's just kind of quivering, it's not doing its thing, because there's not a good regular conduction from the sinoatrial node to the AV node.

    08:27 AV node then fires every now and then when a signal gets through.

    08:33 So you have an irregular heartbeat.

    08:36 So instead being bump, bump, bump, bump, it's bump, bump, bump, bump, bump, bump, bump bump.

    08:44 And that's because of the atrial fibrillation.

    08:47 We will talk more about how that happens in a subsequent discussion you and I.

    08:53 This is ventricular fibrillation.

    08:54 So atrial fibrillation, in most cases can be tolerated.

    08:59 Ventricular fibrillation is what happens just before you die.

    09:03 So instead of having a nice contractile function, providing blood supply to the entire body, including the brain, kidney, and liver, and all those other important structures.

    09:11 Now the heart is quivering.

    09:12 So there is no longer a coordinated contraction, there's no longer blood pressure.

    09:17 And with about 1-2 minutes of this fibrillation, there's not any perfusion to the brain and the brain checks out and you formally die.

    09:26 So V-fib (ventricular fibrillation) is a lethal rhythm.


    About the Lecture

    The lecture Elements of the Heart: Collateral Circulation, Valves and Conduction System by Richard Mitchell, MD is from the course Structure-Function Relationships in the Cardiovascular System.


    Included Quiz Questions

    1. In 90% of the population, the posterior descending artery is a branch of the right coronary artery.
    2. In 90% of the population, the aorta has two right coronary artery branches.
    3. In 90% of the population, the posterior descending artery is a branch of the right circumflex artery.
    4. In 90% of the population, the posterior descending artery is a branch of the left anterior descending artery.
    5. In 10% of the population, the posterior descending artery is a branch of the right coronary artery.
    1. Great cardiac vein
    2. Middle cardiac vein
    3. Small cardiac vein
    4. Vein from the left ventricle
    5. Oblique vein

    Author of lecture Elements of the Heart: Collateral Circulation, Valves and Conduction System

     Richard Mitchell, MD

    Richard Mitchell, MD


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